Field of the Invention
The present invention relates to an element substrate, a liquid discharge head, and a printing apparatus, and particularly to, for example, an element substrate integrating a plurality of electrothermal transducers and driving circuits for driving the transducers, a liquid discharge head integrating the element substrate, and a printing apparatus using the head as a printhead.
Description of the Related Art
As a method of driving an inkjet printhead (to be referred to as a printhead hereinafter), there is known a thermal driving method in which print elements are provided at portions communicating with orifices for discharging ink droplets, a current is supplied to the print elements to generate heat, and then ink droplets are discharged by film boiling of ink. Power is supplied to print elements via the electrode pad of an element substrate integrated in the printhead, and a current is supplied to any desired print elements by time-divisional drive.
Since energy necessary for discharge is different depending on the ink viscosity and discharge amount, it is necessary to optimally design a current to be supplied to the print elements for each ink type. Japanese Patent Laid-Open No. 7-314658 discloses an arrangement for preventing the image quality from degrading due to color difference by changing the plane area of a transistor depending on an ink color.
Furthermore, if the wiring resistance values of a ground wiring and a power supply wiring for supplying power to print elements are different between the plurality of print elements, a voltages applied to each print element changes, resulting in different discharge characteristics. To perform stable ink discharge and improve the image quality of a print image, it is necessary to apply a constant voltage to the plurality of print elements, and it is thus necessary to reduce a change in voltage caused by the resistance difference of the power supply wiring in the element substrate.
Japanese Patent Laid-Open No. 10-044416 discloses an arrangement in which a wiring for applying an externally supplied voltage is divided into a plurality of wirings to equalize voltage drops from an electrode pad to respective print elements. It is possible to divide a plurality of print elements into a plurality of groups, and equalize the resistance values of the divided wirings, thereby equalizing voltages applied to the print elements of each group. Furthermore, it is possible to eliminate the difference between a voltage drop when driving one print element and that when driving all the print elements by time-divisional drive of driving only one print element in one group at once.
In recent years, there is proposed a full-line printhead whose printing width corresponds to the width of a print medium by arranging a plurality of element substrates. The full-line printhead can perform high-speed printing, and is thus used in a printing apparatus for professional use or industrial use.
FIG. 11 is a view showing the arrangement of a full-line printhead formed by arranging a plurality of element substrates in line in a printing width direction.
As shown in FIG. 11, each element substrate 502 having a shape of a parallelogram includes a plurality of print element arrays 504, and respective signals and power are supplied from a printing apparatus (not shown) to electrode pads 505 via a connector 503 and head wirings 506. Furthermore, by connecting and arranging the element substrates 502 (in this example, four element substrates 502) in line, it is possible to decrease the size (H) of one side of the printhead 501. Since the connected portion of each element substrate 502 has a shape having an angle in the printing width direction (W), and the plurality of element substrates 502 can be arranged close to each other, it is possible to reduce the number of print elements arranged to overlap each other in the connected portions of the element substrates 502. Note that to connect and arrange the element substrates 502 in line, the electrode pads 505 need to be arranged around an end portion of each element substrate in parallel to the print element arrays 504.
FIG. 12 is a view showing the arrangement of a full-line printhead formed by arranging a plurality of element substrates in a staggered pattern in the printing width direction. Note that in FIG. 12, the same reference numerals as in FIG. 11 denote the same portions and a description thereof will be omitted.
To obtain satisfactory discharge characteristics, it is necessary to arrange neighboring element substrates close to each other even in the arrangement in which the element substrates 502 are arranged in a staggered pattern. With an arrangement in which the electrode pads 505 are arranged in a direction perpendicular to the direction of the print element arrays 504, it is impossible to ensure a region for head wirings from the electrode pads 505 to the connector 503. Therefore, as shown in FIG. 12, even in the arrangement in which the element substrates are arranged in a staggered pattern, it is necessary to arrange the electrode pads 505 in parallel to the print element arrays 504.
As described above, in the arrangement in which the electrode pads are arranged in parallel to the print element arrays, it is possible to shorten the length of a power supply wiring by arranging the power supply wiring between ink supply ports for individually supplying ink to the print elements. In this way, by reducing a voltage drop caused by the resistance of the power supply wiring in the element substrate, it is possible to increase the speed of high-quality printing, and improve the durability of the printhead.
However, the distance between the ink supply ports depends on the arrangement pitch of the print elements. Therefore, unlike Japanese Patent Laid-Open No. 7-314658, it is impossible to divide a power supply wiring into a plurality of wirings to fit in the wiring resistances. Consequently, the power supply wiring resistances to the print elements are different for each print element array, and voltages applied to the corresponding print elements are different.